Anatomical, physiological and behavioral studies will be carried out on the bat, Pteronotus p. parnellii. This species emits intense sonar signals that contain both frequency modulated (FM) and constant frequency (CF) components. Electrodes will be permanently implanted within the greatly hypertrophied cochlea of this bat and the cochlear potentials will be recorded over extended periods of time in unanesthetized preparations. Particular attention will be directed to the sharply tuned portion of the bat's audiogram and to factors known to affect sharp tuning (temperature, anesthesia, peripheral ear structures and overstimulation). Structural correlates of the sharp tuning will be assessed by studying surface preparations and sections of the organ of Corti with the light and scanning electron microscope. Sharp tuning at the receptor level will be eliminated by overstimulation and the acoustic behavior of the animal will be studied under conditions of obstacle avoidance and insect detection, pursuit and capture. Cochlear potentials will be recorded in flying animals with the aid of miniature telemetry systems. The possible significance of the pulse CF will be studied by determining the physical properties of CF echoes returning to the bat's ear; particular attention will be focused on Doppler shifts due to insect wing beat patterns and on possible signatures created by these patterns. Field studies will be used to determine how, where, and what these animals normally hunt.